Figure 4. Grand mean probability of happy face percepts (Task 1, dashed traces) ± SEM (ordinate) and sigmoidal fits (continuous traces) from the Full-Range Condition (red traces) and the Half-Range Condition (blue traces) as functions of the mouth curvatur of the different Mona Lisa stimuli (abscissa).

(b) The related reaction times (Task 1, triangles, ordinate on the right) and participants confidence ratings (Task 2, stars, ordinate on the left) of their perception responses. Happy and sad variants of the original Mona Lisa image²⁵ (S9) were created in Dr. Kornmeier’s lab. Differences between sigmoid functions (a) are clearly visible and correspond to the differences in reaction time and confidence level traces (b).